Influence of shaped boundaries on propagating compaction bands in brittle porous media.

The compression of brittle porous media can lead to the propagation of compaction bands. Although such localization phenomena have been observed in different geometries, including cuboidal and axisymmetric uniaxial compression, the role of boundary geometry on compaction features has yet to be explored, despite its relevance in geological conditions and industrial processes. To this end, we investigate the influence of shaped boundaries and inhomogeneous inclusions in a model brittle material made of puffed rice cereal. Using a variety of geometries, we show that compaction bands assume the shape of nearby boundaries, but return to a default planar form a distance away from them. Remarkably, the band aligns parallel to characteristic lines of minor principal stress obtained from a simple linear elastic model. The compelling correlation between the rotation of the principal stress directions and compaction band orientation holds implications for the geological interpretation of localized patterns in rocks and for comprehending the formation of weak planes in pharmaceutical tablets.

Evidence That Strain-Rate Softening Is Not Necessary for Material Instability Patterns.

Strain-rate softening has been associated with a wide variety of material instabilities, from the Portevin-Le Chatelier effect in metal alloys to stick-slip motion in crust faults. Dynamic instability patterns have been recently discovered in brittle porous media: diffused, oscillatory, and erratic compaction. Using model simulations inspired by experiments with puffed rice, we question the link between these dynamic patterns and strain-rate sensitivity in such media. An important feature of our model is that it can recover strain-rate softening as an emergent phenomenon, without imposing it a priori at its microstructural scale. More importantly, the model also demonstrates that the full range of dynamic patterns can develop without presenting macroscopic strain-rate softening. Based on this counterexample model, we therefore argue that strain-rate softening should not be taken as a necessary condition for the emergence of instability patterns. Our findings in brittle porous media have implications on models that require strain-rate softening to explain earthquake and metal alloy instabilities.

Plankton filtration with compressible crumb rubber packs.

The experiments described provide insight into the feasibility of using compressible particulate packs to filter live plankton. The pore constriction sizes are controlled by subjecting the filter pack to isotropic confinement, thereby allowing for: (1) enhanced filtration upon confinement and (2) enhanced unclogging upon relaxation. Results show that filtration efficiency increases with increasing confinement; however, complete plankton retention is difficult to attain due to the plankton's ability to pass through pore constrictions that are smaller than the plankton size. The results are anticipated to offer potential benefits to ballast treatment and aquatic filtration operations.

Characterizing potential water quality impacts from soils treated with dust suppressants.

Two separate laboratory experiment series, surface runoff and steady-state seepage, were performed to determine if dust suppressant products can be applied to soils with an expected minimal to no negative impact on water quality. The experiments were designed to mimic arid field conditions and used two soils (clayey and sandy) and six different dust suppressants. The two experiments consisted of: (i) simulated rainfall (intensities of 18, 33, or 61 mm h(-1)) and associated runoff from soil trays at a surface slope of 33%; and (ii) steady-state, constant head seepage through soil columns. Both experiment series involved two product application scenarios and three application ages (i.e., to account for degradation effects) for a total of 126 surface runoff and 80 column experiments. One composite effluent sample was collected from each experiment and analyzed for pH, electrical conductivity, total suspended solids (TSS), total dissolved solids, dissolved oxygen, total organic carbon, nitrate, nitrite, and phosphate. Paired t tests at 1 and 5% levels of significance and project specific data quality objectives are used to compare water quality parameters from treated and untreated soils. Overall, the results from this laboratory scale study suggest that the studied dust suppressants have minimal potential for adverse impacts to selected water quality parameters. The primary impacts were increased TSS for two synthetic products from the surface runoff experiments on both soils. The increase in TSS was not expected based on previous studies and may be attributed to this study's focus on simulating real-world soil agitation/movement at an active construction site subjected to rough grading.